Like a lot of others, I also feel that this would be a great topic to discuss and one I would definitely listen to.
I think that there are a lot of shared experiences that people of certain genders/races/cultures have, and by hiring a person of that gender/race/culture they would be coming in with a view of that shared experience which would help them to create a book that can relate to those genders/races/cultures more authentically than if made by someone who has not had these experiences. Although I think it's all really dependent on the subject matter. If you're asked to create an educational book illustrating aspects of a certain culture, I feel this can be achieved by anyone with the right research. However, if the content is geared more towards the experience a character has while growing up that is prevalent to a particular culture/race, it might be better to have someone of the same culture/race who can empathize with that content to create illustrations for it. Perhaps if the content was about a shared experience or an experience the artist/author is able to research well or get insight from people who had experienced it, it could be illustrated by anybody. Overall though, I think representation in children's books is important and having characters that resemble the children we meet in life helps them to feel included and connected to the stories we read them. I would also like to think that it helps other kids develop empathy and sympathy by allowing them to relate to characters that don't look or act like they do.
Two writers/illustrators that come to mind for this topic would be Ezra Jack Keats (he was mentioned in a previous comment as well) and Lio Lionni (particularly his book Little Blue and Little Yellow).